Thermal hydraulic were a neat idea. They had a solenoid that was filled with a chemical (not sure what, some sort of wax I suppose) that when heated by electrical current would melt and allow the valve to open. The valves opened and closed r e a l s l o w l y. Rain Bird purchased the Thermal Hrdraulic Co in 1967. From what I remember my dad telling me, RB discontinued the valve because there was an issue where some jackass connected them to line voltage which caused the TH solenoid to explode... I think a lawsuit may have followed. I'm not sure how accurate that story was but that was what I had heard. When I was about 6 or 7 my dad gave me a cutaway of a brass TH valve that showed the entire inner workings of it. Too bad I didn't know any better at that age to appreciate it more or I might still have it. We had some in operation on one of the RB properties all the way up to the late 80's if I recall. They also required a fair amount of amperage to operate as well so you typically had to use them with an RC series mechanical controller with the bigger transformer in them.

wow. i may be young but have been around for 15 or so years. ive seen a lot in the field and read and researched a lot more. i feel there is very little i've come across or will come across that is different, new, etc.

Thermal hydraulic solenoids are something i have never heard of and sounds really interesting. it's always exciting to hear about different things in the industry besides rotors, sprays, and drip. its also cool to be reminded every once in awhile that there existed a whole other generation of irrigation prior to the one that i know.

Thermal Hydraulic is the only name I ever heard used in connection with them. They'd never fly in today's energy-efficient world.

Another cool old-school item in the Rainbird lineup was a very special under-head valve that would remain tightly closed until the pressure in a zone exceeded a set point (30 or 40 psi, I think) - then the valve opens fully ~ the idea of the special valve was to compensate for weak systems that couldn't raise all the heads in a zone simultaneously (impact heads, almost certainly, with a sizable flow-by before popping up and sealing)